Regenerative selector magnet driver



May 1 7, 1966 W. G. DOSSE REGENERATIVE SELECTOR MAGNET DRIVER FiledApril 9, 1963 INVENTOR I WlLLIAM G. DOSSE ATTORN United States Patent3,251,941 7 REGENERATIVE SELECTOR MAGNET DRIVER William G. Doss,Chicago, 11]., assignor to Teletype Corporation, Skokie, 111., acorporation of Delaware Filed Apr. 9, 1963, Ser. No. 271,623 8 Claims.(Cl. 17833) by a stop pulse.

The information pulses assume one or the other of two current conditionscorresponding to the information they represent; the start pulse alwayshas one of the two current conditions; and the stop pulse always has theother current condition. The stop pulse maintains the coil in anenergized condition which continues until a start pulse is received. Thestart pulse deenergizes the coil, causing the selector magnet to releaseits armature to initiate operation of the teletypewriter machine. Eachof the information pulses, in sequence, causes the selector magnet coilto be energized or deenergized in accordance with the informationrepresented thus causing the armature to be pulled up or releasedaccordingly. After the selector magnet has positioned the armature,mechanical locking levers associated with the selector cams of theteletype'writer machine move above or below the armature (depending onwhether a mark or space pulse is received) to lock the armature intoposition during the selector interval.

This type of operation is more fully described in United States PatentNo. 2,339,313 issued to W. I. Zenner on January 18, 1944.

If the incoming signal is so distorted that it is only accurate atpoints very near the exact center of each incoming pulse, the mechanicallocking levers may not move in time to prevent an error from occurringdue to false operation of the selector magnet since the locking leverscannot be economically manufactured with sufficiently close tolerances.This problem is further increased in teletypewriter machines which use adifferent locking lever for each diiferent pulse or level of theincoming signal group or character, due to the fact that each of thesedifferent levers has a different tolerance.

The accuracy of high speed teletypewriter receiving equipment can beincreased by using expensive manufacturing techniques to make thetolerances of each of the locking levers the same and to cause thesetolerances to be close so that errors of the above type are eliminated.The cost of solving the problem in this manner is prohibitive whenpresently known manufacturing techniques are used.

Another method for solving this problem caused by dis torted receivedsignals is to provide a regenerative repeater at the receiver forreshaping the signal, in a manner well known in the art, before applyingit to the selector magnet driver. A disadvantage present in thissolution is that a relatively large number of electronic components orrelays must be used in addition to those hold the armature locked inposition until the midpoint of the next incoming pulse.

It is a further object of this invention to combine the 7 features of aregenerative repeater and a selector magnet driver into a single circuitutilizing only a few more components than are necessary for the selectormagnet driver alone.

It is yet another object of this invention to provide a regenerativeselector magnet driver operated in synchronism with the rotation of theselector cam shaft for rendering the selector magnet driver responsiveto the input signals only at the midpoint of each pulse interval, afterwhich, for approximately a full pulse interval, the driver remains setto the condition it attained during the time that the circuit wasallowed to be responsive to the input signal.

These and other objects are accomplished in accordance with a preferredembodiment of this invention in which a normally open switch is placedbetween the source of received telegraph signals and the selector magnetdriver circuit. A timing cam having a plurality of notches cut in itsperiphery is mounted on the selector cam shaft and rotates therewith.The cam follower comprises one of the switch contacts; and whenever thefollower encounters one of the notches, the switch is closed momentarilyto be reopened by the cam as it continues its rotation. As a result, theinput signals are applied to the selector magnet driver only during thebrief intervals when the follower contact falls into one of the notchesin the cam.

When the switch is closed, the received signal is applied to theenergizing circuit for the coil of the selector magnet; and this circuitfunctions as a conventional Schmitt trigger, well known in the art, toenergize and deenergize the coil. Additional coupling elements have beenprovided in the trigger circuit which cause the circuit to function as abistable multivibrator whenever the switch contact is reopened by thetiming cam. This bistable multivibr-ator remains set to the stable statewhich corresponds to the setting of the circuit functioning as aSchrnitt trigger just prior to the opening of the contact.

The notches in the timing cam are cut so that the switch is closed atthe midpoint of each pulse in each incoming pulse group. Thus, theselector magnet coil remains energized or deenergized in accordance withthe received signal present when the switch was last closed throughouteach pulse interval until the next closure of the switch which occurs atthe midpoint of the next pulse interval. In this manner the signal isregenerated simultaneously as it is used to operate the selector magnetcoi-l, since for the major portion of each pulse interval the system isheld nonresponsive to the input signals in the manner of a regenerativerepeater. When the input signals are applied to the driving circuit ofthis invention, they override its operation as a bistable multivibratorcausing it to function as a Schrnitt trigger circuit.

Further objects and features of this invention will become apparent tothose skilled in the art upon consideration of the following detaileddescription taken in conjunction With the accompanying drawing, thesingle figure of which shows a circuit diagram of a preferredembodiment' of the invention.

Referring now to the drawing, there is shown a pair of line inputterminals 10 and 11 to which are applied the incoming or receivedtelegraph signals. For the purpose of this discussion, assume that amark on the line is represented by current flowing on the line and thata space -is represented by a no current condition. When a mark ispresent on the line, current flows from terminal 10 through the parallelconnection of resistor 12 and a set of diodes called click suppressors13 to terminal 11 thereby causing a voltage drop to take place acrossthe 3 7 click suppressors 13 and the resistor 12. Details of thefunction of these click suppressors are given in the copendin'gapplication Serial No. 196,384 to C. R. Winston, filed May 21, 1962.

The voltage at the junction 14 between the click suppressors 13 isapplied to the base of a transistor 15 through a switch 16 which isoperated by aVtiming cam 17 mounted on the selector cam shaft 18 of asuitable teletypewriter receiver such as the telegraph printer shown inthe aforementioned Zenner patent. The portion of the printer describedin the Zenner patent which is neces sary to an understanding of theinvention has been shown in the drawing and includes a selector camshaft 18, a clutch 19 and the selector cams 20 to which has been added atiming cam 17 in accordance with this invention.

Prior to the receipt of the first group of pulses, the cam shaft 18 isstationary and the timing cam 17 is positioned so that a follower 21rests on the relatively wide cut out portion 36 of the cam 17. The cutout portion 36 has sufficient width to cause the follower 21 to ride onit during the stop, start, and the first half of the first informationpulse of each group. This causes the switch 16 to be closed during thistime rendering the drive circuit responsive to input signals ashereinafter explained. When a start pulse is received, it is representedas a space or no current condition on the line; so that no potentialdrop takes place across the click suppressors 13 as a result of linecurrent. This allows the negative potential from the battery 24 to beapplied through the now closed switch 16 and the resistor 29 to the baseof the transistor 15 causing it to conduct, since this negative,potential causes the base of the transistor to be biased negatively withrespect to its emitter. When the transistor 15 conducts, the potentialon the base of the transistor 23 rises and causes that transistor to becut off thereby releasing or deenergizing the selector magnet coil 28 ina manner which will be explained more fully hereinafter.

The release of the selector magnet 28 by this action causes the camshaft 18 to commence rotation as is more fully described in theaforementioned Zenner patent. The follower 21 rides on the cut outportion 36 of the timing cam 17 during the entire start pulse intervaland through the first half of the first information pulse of the group,at which time it is raised by the cam 17 to open the switch 16. Thiscauses the selector magnet driving circuit to be nonresponsive tofurther input signals until the switch 16 is once again closed by thefollower 21 falling into the next one of the cut out portions 22 on thetiming cam 17.

When the switch 16 is closed by means of the follower 21 falling intoone of the slots 22. on the timing cam 17,

the voltage present on the terminal 14 is applied to the base of thetransistor 15. If there is a mark on the line (current flowing throughthe click suppressors 13), the voltage on the terminal 14 rises causingthe base of the transistor 15 to become positive relative to itsemitter, thereby turing the transistor 15 off. This in turn causes thepotential on the collector of the transistor 15 to drop thereby biasingthe transistor 23 into conduction. When the transistor 23 conducts,current flows from the battery 24 through the common emitter resistor25, a click suppressor 26, the transistor 23, a current limitingresistor 27, and the energizing coil 28 of the selector magnet to thenegative terminal of the battery 24. This causes the coil 28 of theselector magnet to be energized in accordance with a mark appearing onthe line between the terminals 10 and 11.

Following this energization, the timing cam 17 continues to rotate inthe directi'on'of the arrow with the ratation of the selector cam shaft,causing the follower 21 to open the contacts of the switch 16 therebyrendering the driving circuit, comprised of the transistors 15 and 23,insensitive to further input signals. en this occurs, the circuitcomprised of the transistors 15 and 23 operates as -a bistablemultivibrator or flip-flop due to the crosscoupling effected by thedirect connection between the collector of the transistor 15 and thebase of the transistor 23 and the connection between the collector ofthe transistor 23 and the base of the transistor 15 through a pair ofresistors 29 and 3t} and a pair of diodes 31. An additional resistor 32is connected between the positive terminal of the'battery 24 and thejunction between the resistors 29 and 31) to provide operating bias forthe circuit when it functions as a bistable multivibrator. When thesignal on the line just prior to the opening of the switch 15 is a mark,as discussed previously, the transistor 15 is turned off and thetransistor 23 is rendered conductive. At the time the switch 15 opens,the potential on the collector of the transistor 23 is high and thispotential is coupled through the resistors 29 and 30 and the diodes 31to the base of the transistor 15 to maintain the transistor 15 biased tononconduction. The driving circuit will remain set to this state untilthe switch 16 is again closed.

If, at the time the follower 21 falls into the next slot 22 to close theswitch 16, the input signal is a space (no current on the line betweenterminals 10 and 1-1), the potential on the base of the transistor 15drops to near the negative potential of the battery 24 causing thetransistor 15 to be rendered conductive thereby overriding the bistablecircuit characteristics which exist when the switch 16 is open. Thecircuit now functions as a Schmitt trigger and the rise in potential onthe collector of the transistor 15, caused when it becomes conductive,is applied to the base of the transistor 23 and renders it nonconductivedue to the fact that the potential on the base of the transistor 23 isdriven positive with respect to the potential on the emitter of thattransistor.

In order to assume that the transistor 23 is cut 0E when the transistor15 is rendered conductive, the click suppressor 26 has been provided inthe connection between the emitters of the transistors 15 and 23. Thisclick suppressor causes a slight drop in potential to occur and forcesthe emitter potential of the transistor 23 to be below the potentialapplied to its base from the collector of the transistor 15 when thetransistor 15 conducts. If the click suppressor 26 were not provided,the potentials on the emitter and base of the transistor 23 would bealmost the same when the transistor 15 became conductive; and thetransistor 23 possibly might not be rendered nonconductive. The clicksuppressor 26 prevents this from happening.

When the transistor 23 is rendered nonconduotive, the energizing currentpath for the selector magnet coil 28 is broken causing the selectormagnet coil 28 to be deenergized. The selector magnet coil 28 opposesthe change in current which has occurred and applies a transient to thecollector of the transistor 23 which is more negative than the potentialat the negative terminal of the battery 24. This causes a diode 33 toconduct to pass the transient through a resistance capacitance cirouit,comprised of a resistor 34 and a capacitor 35, which limits thetransient to a value below the breakdown voltage of the transistor 23while the energy in the coil 28 is being dissipated.

The cam 17 continues to rotate with the selector cam shaft, and the camfollower 21 rises out of the notch 22 opening the switch 16 renderingthe circuit nonresponsive to input signals. When this occurs, thecircuit once again operates as a bistable multivibrator with therelatively positive potential on the collector of the now conductingtransistor 15 applied to the base of the transistor 23 maintaining thetransistor 23 in its nonconductive state. The circuit will remain set tothis space condition until the switch 16 is closed by the action of thefollower 21 falling into the next slot 22 which then renders the circuitresponsive to .the input signal present at that time and causes thecircuit to operate as a Schmitt trigger.

The sequence of operation described previously continues throughout eachpulse interval of the incoming pulse group or character. The notches 22out in the periphery of the timing cam 17 are spaced so that the switch16 is closed just prior to the midpointof each pulse interval and isopened at the midpoint of each pulse interval of the incoming signal.When a complete character has been received, the switch 16 comes to restin a closed position due to the fact that the follower 21 now rests inthe relatively wide cut out portion 36 of the timing cam 17. The switch16 then remains closed during the stop, start and the first half of thefirst information pulse of the next group, and the sequence of operationjust described is repeated for the next group or character.

The use of this circuit removes the locking control of the selectormagnet armature from the inaccurate mechanical locking levers presentlyin telegraph printers to the relatively accurate control of the timingcam 17. It

-is possible, with present manufacturing techniques to manufacture thecam 17 with much closer tolerances at a lower expense than it is tomanufacture mechanical locking levers with the same close tolerances.The system of this invention reduces errors caused by badly distortedsignals in this conventional telegraph printers presently in use in highspeed telegraph systems.

The diodes 31 which have been provided in the path coupling thecollector of the transistor 23 to the base of the transistor may beeliminated if desired. However, these diodes give a constant voltagedrop over a wide range of current flowing through them in the forwarddirection and compensate for the value of the resistor 30 necessary toprovide theproper bias onthe base of the transistor 15.

It should be noted that the mechanical switch 16 may be replaced with aphotocell or other suitable switching means operated in synchronism withthe selector cam shaft 18. The characteristics necessary for suchswitching means are that under certain conditions it must exhibit a highresistance (open) and under other conditions it must exhibit a lowresistance (closed). The use of the term switc in the claims is intendedto encompass these alternatives.

While this invention has been described-in conjunction with a specificembodiment, it will be apparent to those skilled in the art that variousmodifications and changes may be made in the specific circuit andapparatus shown without departing from the spirit and scope of theinvention.

What is claimed is:

1. A regenerative driving circuit for the selector magnet of a telegraphreceiver having a timing cam shaft therein including (a) a source ofinput signals,

(b) means for energizing the selector magnet in response to inputsignals above a predetermined magnitude and for causing the selectormagnet to be deener-gized in response to input signals below thepredetermined magnitude,

(c) a normally open switch connected between the source of-input signalsand the energizing means,

(d) timing means controlled by the rotation of the timing cam shaft forperiodically closing the switch to allow the input signal present at thetime during which the switch is closed to be applied to the energizingmeans, and

(e) means operable when the switch reopens for causing the energizingmeans to remain set to the condition of operation it attained when theswitch was closed.

2. A regenerative driving circuit for the selector magnet of a telegraphreceiver having a selector cam shaft therein including (a) a source ofbinary signals arranged in permutation code,

(b) means for energizing the selector magnet in response to binarysignals of one type and for causing the selector magnet to be'deener-gized' in response to binary signals of another type,-

(c) a normally open switch connected between the source of binarysignals and the energizing means,

(d) timing means controlled by the position of the selector cam shaftfor periodically closing-the switch to allow the binary signal presentat the time of closure to be applied to the energizing means, and

(e) means operable when the switch reopens for caus-,

ing the energizing means to remain set to the condition of operation itattained when the switch was closed.

3. Telegraph receiving apparatus having a selector cam shaft and aselector magnet with an energizing coil therein including i (a) acircuit for energizing the coil of the selector magnet in response toinput binary signals,

(b) a timing cam on the selector cam shaft,

(c) a switch operated by the timing cam and closed only at predeterminedintervals established by the position of the timing cam to render theenergizing circuit responsive to the input signals, the energizingcircuit operating as a Schmitt trigger when the switch is closed, and

(d) means for causing the energizing circuit to operate as a bistablemultivibrator when the switch is open,

the energizing circuit being set .to the stable state which correspondsto the setting of the circuit functioning as a Schmitt trigger justprior to the time the switch is opened.

4. A regenerative driving circuit for the selector magnet of a telegraphreceiver having a selector cam shaft therein including (a) a source ofinput signals,

(b) a circuit operating as a Schmitt trigger for energizing the selectormagnet in response to input signals above a predetermined magnitude andfor causing the selector magnet to be deenergized in response to inputsignals below the predetermined mag nitude,

(c) a normally open switch connected between the source of input signalsand the energizing circuit,

((1) timing means operated in synchronism with the rotation of theselector cam shaft for periodically momentarily closing the switch toallow the input signal present duringthe time the switch is closed to beapplied to the energizing circuit, and

(e) means operable when the switch reopens after each closure forcausing the energizing circuit to function as a bistable multivibratorremaining set to the condition the circuit attained when the switch wasclosed.

5. Apparatus according to claim 4 in which the input signals are binarysignals arranged in permutation code. 6. A regenerative driving circuitfor the selector magnet of a pulse communication receiver having aselector cam shaft therein including (a) a source of binary input pulsesarranged in permutation code,

(b) a circuit for energizingthe selector magnet in response to inputbinary pulses having a magnitude above a predetermined level and forcausing the selector magnet to be deenergized in response to inputpulses having a magnitude below the predetermined level,

(c) a normally opened switch connected between the source of inputsignals and the energizing circuit,

(d) a timing cam operated in synchronism with the rotation of theselector cam shaft for periodically momentarily closing the switch onceduring each binary pulse to allow the input signal present during thetime the switch is closed to be applied to the energizing circuit, and

(e) means operable when the switch reopens after each closure thereoffor causing the energizing cir- 7 cuit to remain set to the conditionthe circuit attained during the time the switch was closed,

7. A system in accordance with claim 6 wherein the energizing circuitfunctions as a Schmitt trigger when the switch is closed and functionsas a bistable multivibrator when the switch is open.

8. A regenerative driving circuit for the selector magnet of a telegraphreceiver having a selector cam shaft therein including (a) a source ofbinary pulse input signals arranged in permutation code,-

(b) a circuit operating as a Sch-mitt trigger for energizing theselector magnet in response to input pulses of one type and for causingthe selector magnet to be deenergized in response to input pulses of asecond type,

(c) a normally open mechanical switch connected between the source ofinput pulses and the energizing circuit,

(d) a timing cam operated in synchronism with the rotation of theselector cam shaft and having a plurality of slots cut in the peripherythereof for pcriodically momentarily closing the switch once during eachinput pulse to allow the input pulse present during the time the switchis closed to be applied to the energizing circuit setting it inaccordance therewith, and

(e) additional means operable only when the switch reopens followingeach momentary closure for causing the energizing circuit to function asa bistable multivibrat-or remaining set to the condition the Britt178-70 20 NEIL C. READ, Primary Examiner.

ROBERT H. ROSE, Examiner. A I. DUNN, T. B. HABECKER, AssistantExaminers.

1. A REGENERATIVE DRIVING CIRCUIT FOR THE SELECTOR MAGNET OF A TELEGRAPH RECEIVER HAVING A TIMING CAM SHAFT THEREIN INCLUDING (A) A SOURCE OF INPUT SIGNALS, (B) MEANS FOR ENERGIZING THE SELECTOR MAGNET IN RESPONSE TO INPUT SIGNALS ABOVE A PREDETERMINED MAGNITUDE AND FOR CAUSING THE SELECTOR MAGNET TO BE DEENERGIZED IN RESPONSE TO INPUT SIGNALS BELOW THE PREDETERMINED MAGNITUDE, (C) A NORMALLY OPEN SWITCH CONNECTED BETWEEN THE SOURCE OF INPUT SIGNALS AND THE ENERGIZING MEANS, (D) TIMING MEANS CONTROLLED BY THE ROTATION OF THE TIMING CAM SHAFT FOR PERIODICALLY CLOSINGK THE SWITCH TO ALLOW THE INPUT SIGNAL PRESENT AT THE TIME DURING WHICH THE SWITCH IS CLOSED TO BE APPLIED TO THE ENERGIZING MEANS, AND (E) MEANS OPERABLE WHEN THE SWITCH REOPENS FOR CAUSING THE ENERGIZING MEANS TO REMAIN SET TO THE CONDITION OF OPERATION IS ATTAINED WHEN THE SWITCH WAS CLOSED. 